2021 SASS Bio TYS P2 Ans

2021 O Level Mark Scheme – CT and Markers’ Report Paper 2 S/N Answer Comments and explanation 1a P: vena cava Q: right atrium - b - Transport blood rich in oxygen and nutrients from aorta - To cardiac/heart muscles - c - Oxygen dissolves in the moisture lining the alveolar walls and then - Diffuses into the blood capillaries - Oxygen combines with the haemoglobin in red blood cells to form oxyhaemoglobin at the lungs, where oxygen concentration is high - Oxygen is carried in the form of oxyhaemoglobin from the lungs to the left atrium of the heart via pulmonary vein - Blood rich in oxygen is pumped into the left ventricle and out of the heart via the aorta - Aorta transports blood to the kidney via the renal artery - At the kidney, where oxygen concentration is low, oxyhaemoglobin releases oxygen, - which then diffuses through the walls of the blood capillaries into the cells of the tissues. No need for excessive details about the oxygenation of blood in the lungs. Route to the kidneys is important. Crucial to refer to the renal artery and the correct side of the heart. d - damaged tissues and platelets produce thrombokinase - thrombokinase converts inactive prothrombin into active thrombin in the presence of calcium ions - thrombin catalyses the conversion of the soluble protein fibrinogen into insoluble fibrin threads - to form a mesh to trap blood cells. 2a i) 6 x 2.5 = 15 au/year ii) Heat iii) 20 x 2.5 = 50 au/year b Percentage transferred = 15 / 90 x 100 = 16.7% C - For animals to move, they must release more energy via aerobic respiration for muscle contraction. - By reducing movement of animals, less energy is lost as heat to the surroundings, - this allows more energy to be used for growth 3a B, salivary amylase C: pancreatic/intestinal lipase A: pepsin - b - Enzymes involved in digestion catalyse catabolic reactions - By lowering the activation energy of the digestion reaction Common mistakes: to list a range of digestive enzymes and their associated substrates and products, referencing to

- Substrate, e.g. starch - with a 3-D shape complementary to the active site of the - enzyme, e.g. amylase, - will fit into amylase to form an enzyme-substrate complex - chemical reaction occurs, substrate is broken down by enzyme into products e.g. maltose - products leave the active site of enzyme and enzyme remains chemically unchanged optimal pH values and possible denaturation 4a - Nn x Nn - N, n, N, n - NN, Nn, Nn, nn - Normal, normal, normal, PKU “carrier” is not acceptable for phenotype. Similarly, “affected” is less ideal compared to “PKU”. b - 25% or 1 in 4 or 1/4 c - Mother’s bloodstream would possess the enzyme - Amino acid phenylalanine from fetal blood diffuses into maternal bloodstream - via the placenta - Enzyme would then be available in mother’s body to break down phenylalanine Note: Enzymes are too large to diffuse into fetal bloodstream. It is the amino acids that diffuse from fetus to mothe